How to calculate force required for gas springs

[sloughboy]

I am planning on using gas springs to assist in the lifting and then holding up the pop-up portion of my trailer. I imagine the pop-top will weigh no more than 60lbs. Two questions. First. Should I place two gas springs on the front and two gas springs on the rear of the trailer, or should I place the same number on the left and right side. The attached drawings shows the gas springs on the front (note they will be placed inside the trailer but are shown on the outside for clarity). Second. How can I calculate the force required. I looked at a number of online sites, but there is no direct calculation for this type of application. I wish I could just use actuators but I want to keep the weight down. Thanks a bunch.

 

[nated]

The roof appears to lift 16", but you're only using a 10" stroke gas shock? If you use 4 100 lbs shocks together, you'll need that much force to close the roof also.

 

[john61ct]

The force should handle the load plus just a bit.

 

[jwiereng]

I think the force required to close the top would be roughly equal to the sum of all the springs(gas) minus the mass of the lid.

Example 200 lbs lid with 4 x 60 lbs springs would take 40 lbs force to close.

This assumes the springs are vertical. I think Angle force would require trigonometry to calculate.

Keep in mind snow loading, if that is relevant to your camping locations.

 

[dman93]

Since the springs are at an angle you can’t avoid doing some trigonometry. Four 100 lb Springs seems like way overkill for a 60 lb top. From the picture you showed, the springs are symmetrical and equally arrayed so each spring should just be lifting 15 lb. Closed, they are at about 30°. That means the force is reduced by about 1/2 ... so with a 30 lb spring the lid would stay closed, barely, when you release the latches. As you push or pull it up, as the spring goes more vertical, it provides more assist. At the fully open position, if the springs are at a 45° angle, the force is reduce by about 40% so the four springs provide 30x4 = 120 x .60 = 72 lb, so it would take 12 lb to pull down a 60 lb lid. That doesn’t seem like enough margin to hold it open with racks, snow etc so I would suggest a shorter spring that can be more vertical when open, to provide more support. As soon as you pull the lid down, you gain leverage over the spring and it gets easier to pull. Note all my numbers are rough, it all depends on the exact geometry (angles) and of course the pivot point locations also need to allow the full lid lift (16”) within the the travel of the strut.

 

[Teardropper]

Are you getting anywhere with this? I'm wondering how you are going to seal the raised portion when it's up?